1. Field of the Invention
The present invention relates to a rotary switch for a control unit in which a light-emitting device and a receiver are arranged on a printed circuit board such that switching positions of the rotary switch can be detected optoelectronically.
2. Description of the Background Art
Optical encoders are used to eliminate mechanical tolerances and influences on rotary switches operated according to a principle of signal tapping via contact springs. The optical encoders register a rotational angle and a direction of a rotational movement of bodies in motion. In addition, the optical encoders generally include a light-emitting device, a grid plate such as a grid disk or grid ruler, and a detection device such as a receiver. The grid plate is connected to the body in motion and includes a periodic aperture pattern. Further, light emitted by the light-emitting device is modulated by the grid plate and the detection device detects the modulated light. The detection device then outputs a digital bit pattern based on the detected bit pattern.
A known optical encoder is disclosed in German publication OS 36 32 084. This optical encoder includes an array of periodic optically effective structures, which interact with a radiation source emitting non-parallel radiation, and a radiation receiver rigidly connected with the radiation source. The receiver has at least two receiving elements, which are positioned vertically or nearly vertically to the direction of the motion of the array with the periodic structures. Therefore, to obtain directional data, at least two receiver elements are required to detect the modulation, whereby a phase shift of the received signals is used to measure the direction of the motion.
In addition, a rotary switch having optoelectric capabilities for detecting the motion and direction of the rotary knob is described in the unpublished German Patent Application DE 103 14 315. In this switch, a light source illuminates the rotary knob and the illuminated light is used as part of an encoder for detecting the motion and direction of a rotary actuator or control element of the switch. In more detail, a part of the light emitted by the light source is forwarded to receivers via a light guide or distributor. Thus, the receivers are mounted level with the light source on a same printed circuit board. Then, a digital bit pattern such as a Gray code is generated based on the received light. The generated digital bit pattern is also further processed in subsequent electronics. In this example, the light source, the light distributor, and the receivers form the optical encoder of the rotary switch.